The present invention relates to a portable device used for remote control.
Due to the progress in information communication technology and the widespread use of communication devices, remote control has become popular. Remote control enables a user to remotely control an external device of a vehicle, a house, an electrical appliance, or the like with a portable device so that the external device performs a predetermined action. The portable device transmits a signal, which includes a code corresponding to the operation the user has performed, in a predetermined range. When receiving a signal from the portable device, the external device decodes the code included in the signal to execute a command that is associated with the code. For example, in a keyless entry system, a user approaches a vehicle and pushes an unlock button of the portable device to unlock the vehicle doors. In a smart entry system, the doors are automatically unlocked when a user who is carrying a portable device approaches the vehicle and are automatically locked when the user moves away from the vehicle.
FIG. 1 shows a portable device 80, which remotely controls a vehicle and which is described in Japanese Laid-Open Patent Publication No. 2002-339605. The portable device 80 includes a card-like case 81 accommodating a battery 82 and a circuit board 84 to which a plurality of electronic components are connected. It is desired that such a portable device 80 be made more thin and compact to further improve portability.
The strength of the case 81 of the portable device 80 decreases when the case 81 is thin and made of a synthetic resin. Accordingly, the application of external force may damage the portable device 80. To ensure the strength of the case 81, the case 81 may be made of metal. However, the metal case 81 would block radio waves and lower the signal receiving and transmitting capability of the portable device 80.